Mold releasable pattern material for use in investment casting

ABSTRACT

A composition for use in investment casting includes a pattern material. The pattern material has internal mold releasability. The composition is suitable for use in investment casting. The pattern material may include a wax, a resin, a filler, and/or a fluorochemical. The pattern material may be capable of being injected numerous consecutive times without requiring the application of an external mold release agent (such as spraying silicone release agent) to a die used in the investment casting process. The pattern material would preferably have sufficient mold releasability to not adhere to the die, but sufficient adhesion to adhere to a shell-forming material, such as a ceramic slurry.

BACKGROUND

This application relates to the field of investment casting.Particularly, the application relates to a pattern material and its usein investment casting.

Investment casting, sometimes referred to as the ‘lost wax process’,requires the making of an original pattern typically of patternmaterial, investing or repeatedly dipping the patterns into a refractoryslurry and drying to make a ceramic shell, and melting or burning thepattern material out of the shell leaving a shell suitable for pouringmolten metal.

Initially, before the casting process begins, an injection die isconstructed to produce precise wax patterns. This tool may beconstructed of aluminum or some other material, and may be formed usingCAD/CAM driven CNC milling and EDM machines. The injection die may beautomated and may contain numerous controls and monitoring devices toprovide dimensionally consistent patterns. For many applications, singlecavity dies are used. Multi-cavity dies may also be used (e.g. for highproduction quantities).

A specially formulated pattern material may be injected into a die toproduce the pattern for the part. Typically, one pattern is made foreach finished part to be cast. This pattern is an exact replica of themetal part to be produced, generally with some allowances added tocompensate for volumetric shrinkage during the process. The pattern alsoincludes one or more gates to guide molten metal into the part duringthe solidification process.

In some processes, a system such as that described in U.S. Pat. Nos.4,971,547 or 5,205,969, the disclosures of which are hereby incorporatedby reference, may be used for automatically distributing a semi-solidwax-based pattern material to the injection presses. This system isunique in the industry in its general ability to control patternmaterial temperature within ±1 degree Fahrenheit at a relatively lowtemperature and high viscosity, which is beneficial for producingdimensional conformity between patterns

Pattern material injection molding at this temperature may have severaladvantages. Since the pattern material, in this system, is in asemi-solid state when injected, the part undergoes less shrinkagethrough the freezing process. In turn, the pattern generally possessesbetter dimensional stability and may better resist flash and cavitation(or sink) when cooling.

The individual wax patterns may be assembled onto a wax sprue to form amold, or tree. The number of patterns assembled per mold variesdepending upon the size, weight, and configuration of a given part.

Ceramic molds may be created by dipping or “investing” the assembledpatterns in liquid ceramic slurry, draining and then coating with a dry“stucco” sand. After drying, this process is repeated several timesuntil a specified shell thickness results. The ceramic shell may rangein thickness from 3/16″ to ½″ depending on the size of the part beingproduced.

Robotics may be incorporated into this operation. Sophisticated shelldrying technology may be used to reduce the total time to build a shelland improve quality related to drying defects. The ceramic shells may bedried by moving the molds through forced air drying. Stable, economical,environmentally safe water based slurries may be used to form the shell.

The pattern material may be melted out, leaving a hollow ceramic shell.The molds may be fired at 1600-2000 degrees Fahrenheit to fuse theceramic particles together so that the mold can withstand the pressureand temperature of the molten metal being cast. This also tends toremove any residual wax in the mold.

Molten metal is poured into the pre-heated molds. Typical pouringtemperatures are around 3000 degrees Fahrenheit for steel. Beforecasting, every melt may be analyzed spectrographically to assurecompliance with the necessary specifications.

The ceramic shell may be removed from the metal mold with high-pressurejets of water, which may operate at 8000 to 9000 psi, and/or may bemechanically removed. Any ceramic material remaining in pockets or holesmay be dissolved away in a caustic bath and/or may be mechanicallyremoved to ensure part cleanliness.

The parts are removed from the mold and the material protrusion leftfrom the gate, called the gate witness, may be ground to printspecification using a fixture for repeatability and efficiency.

Parts may be cleaned and receive their final surface finish by eitherblasting with steel shot or abrasive grit. Surface finish rangesgenerally from 90-150 Ra.

In a modern investment casting the making of patterns is often the workof automatic injection presses where a pattern material as liquid orpaste is injected into a die. The injected pattern material may be held,cooled and ejected from the die and may fall into a water bath to coolcompletely. To keep the wax from sticking in the die cavity, a moldrelease agent is typically sprayed onto the die.

The most common mold release agents is silicone, polydimethylsiloxane,either as a water emulsion or as 100% silicone oil. The use of suchmaterials as mold releases greatly degrades the quality of the resultingpatterns due to open knit lines and flow lines. The silicone preventsthe wax pattern material from fusing together during the injectionprocess resulting in open knit lines that reproduce during investing andpouring of metal. Closed knit lines that are greatly weakened by thepresence of silicone mold release may be caused to open during theinjection, assembly, and/or dipping process resulting in open knit linesthat can be reproduced in the finish product.

The process is exacerbated due to the complex patterns that need to beformed. Because of the power of producing near net shape parts thatrequire little if any machining, the parts requirements can be complex.Some dies may have multiple sliding cores, hidden passages, and/or deepslots demanding the wax pattern material conform to these intricateshapes and then cleanly remove from the die. Due to some of these diegeometries, there are areas of some dies that can not be sprayed (or atleast sprayed well) with mold release. The tendency is to over spray toachieve good release and the over abundance of spray within the die is aproblem resulting in open knit lines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a method for investment casting according toone embodiment; and

FIG. 2 is an illustrative diagram of an open knit line.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

A pattern material for use in investment casting may posses the abilityto be released from a mold without the, or with a reduced need for,application/spraying of release agents on a die used to form a patternfrom the pattern material (i.e. the pattern material may have internalmold releasability). The mold release agents which are sprayedon/applied to the die shall be referred to herein as external moldrelease agents (i.e. external to/separate from the pattern material).

In some embodiments, a pattern material includes an additive thatcontributes to the internal mold releasability of the pattern materialand eliminates or reduces the need for spraying of mold release agentsduring the formation of the pattern. Exemplary additives of this typemay include fluorochemicals, such as perfluorinated oils (e.g.perfluoropolyether) with and without functional groups and otherfluorinated compounds. Some fluorochemicals available for use includeFluorogaurd® polymer additive available from Dupont, Novec™fluorosurfactants available from 3M (previously Fluoradgfluorosurfactants), and Zonyl® fluorosurfactants from DuPont. Accordingto some exemplary embodiments, the pattern material may include at leastabout 0.1 wt. % of the mold release additive. In other embodiments, thepattern material include at least about 0.2 wt % or about 0.3 wt. % ofthe mold release additive. According to some exemplary embodiments, thepattern material includes no more than about 1 wt. % of the mold releaseadditive. In other embodiments, the pattern wax material may include nomore than about 0.8 wt. % or up to about 0.6 wt. % of the mold releaseadditive. In some embodiments, the pattern material comprises less than5 wt. % of this additive. Alternatively (or additionally), a patternmaterial may be selected which inherently has a reduced need forspraying of mold release materials.

For pattern materials using internal mold release additives, the abilityto eliminate or reduce the need for spraying may be determined bycomparing the performance of the pattern material without the additiveto the performance of the pattern material with the additive. Adetermination can be made as to how many consecutive quality patternscan be formed with each formulation. A quality pattern is any patternwhich resembles the final part closely enough that it will not result ina rejected part when reproduced. In some embodiments, the patternmaterial formulation with the additive may be used to form at leasttwice as many consecutive quality parts as the pattern materialformulation without the additive. In other embodiments, the patternmaterial formulation with the additive may be used to form at least tentimes as many consecutive quality parts. In some of these embodiments,the pattern material formulation with the additive will be able to forma substantially unlimited number of consecutive quality parts, while thepattern material formulation without the additive will not be able toform a substantially unlimited number of consecutive quality parts.

According to many embodiments, the pattern material with the additivemay be configured such that is has sufficient mold releasability that itis capable of demonstrating one or more of these properties in a die fora typical part used for investment casting. According to someembodiments, the pattern material with the additive may be configuredsuch that is has sufficient mold releasability that it is capable ofdemonstrating one or more of these properties in a die for a complicatedpart (e.g. a part having at least three pins around which the patternmaterial must flow). According to some embodiments, the pattern materialwith the additive may be configured such that is has sufficient moldreleasability that it is capable of demonstrating one or more of theseproperties in a die for a part having a deep draw (e.g. a wall ¼ inchacross, 1.5 inches deep, and about 90 degrees to the parting line).According to still other embodiments, the pattern material with theadditive may be configured such that is has sufficient moldreleasability that it is capable of demonstrating one or more of theseproperties in a die for a part meeting a combination of two or more ofthese parameters. It should be noted that a pattern material may be usedin a die meeting some or none of the above-mentioned parameters, butstill be configured such that it is capable of demonstrating one or moreof these properties in a die according to one or more of the abovementioned parameters.

Some exemplary pattern materials with internal mold releasability mayallow a single die to be used for a large number of shots withoutrequiring a mold release agent to be sprayed or otherwise applied to thedie. According to some embodiments, the pattern material may be used atleast 40 times without application of external mold release agents. Insome embodiments, the pattern material may be used at least about 100times without application of external mold release agents. In stillother embodiments, the pattern material may be used at least about 500times without application of external mold release agents. In anadvantageous embodiment, the pattern material may be used asubstantially unlimited number of times without application of externalmold release agents.

According to many embodiments, the pattern material may be configuredsuch that is has sufficient mold releasability that it is capable ofbeing used in the above-listed number of consecutive shots without theapplication of external mold release in a die for a typical part usedfor investment casting. According to some embodiments, the patternmaterial may be configured such that is has sufficient moldreleasability that it is capable of being used in the above-listednumber of consecutive shots without the application of external moldrelease in a die for a complicated part (e.g. a part having at leastthree pins around which the pattern material must flow). According tosome embodiments, the pattern material may be configured such that ishas sufficient mold releasability that it is capable of being used inthe above-listed number of consecutive shots without the application ofexternal mold release in a die for a part having a deep draw (e.g. awall ¼ inch across, 1.5 inches deep, and about 90 degrees to the partingline). According to some embodiments, the pattern material may beconfigured such that is has sufficient mold releasability that it iscapable of being used in the above-listed number of consecutive shotswithout the application of external mold release in a die for a partmeeting a combination of two or more of these parameters. It should benoted that a pattern material may be used in a die meeting some or noneof the above-mentioned parameters, but still be configured such that itis capable of producing the above-mentioned number(s) of consecutiveshots in a die according to one or more of the above mentionedparameters.

Pattern materials suitable for investment casting would be able to bemolded using a die to form a predictable pattern and would be capable ofbeing removed from a shell without damaging the shell's ability to beused to subsequently form an item.

The pattern material, according to many embodiments, exhibits little orno shrinkage when formed in the die. Linear shrinkage may be measured bycomparing the length of the pattern to the length of the die used toform the pattern. According to some embodiments, the pattern materialhas a shrinkage of no more than about 0.01 inch per inch (inch ofshrinkage per inch of pattern in a given direction). This may bemeasured using a rectangular pattern having a length of 10 inches.According to other embodiments, the pattern material has a shrinkage ofno more than about 0.008 inches per inch or no more than about 0.006inches per inch. According to some embodiments, some pattern materialsmay have shrinkages of 0.002 inch per inch or more and still beacceptable.

In many embodiments, the pattern material is selected to have a low ashcontent. Ash content may be measured as explained bellow. According tosome embodiments, an ash content of a pattern material may be less thanabout 0.02%. According to other embodiments, the ash content may be lessthan about 0.01% or less than about 0.008%. In other embodiments, theash content may be less than about 0.002%. If an additive is used in thepattern material to improve internal mold release, the additive may besubstantially or entirely ash-free (i.e. contributes little or none tothe ash content of the pattern material). The Fluorogaurd polymeradditive from Dupont may be one such additive.

The ash test includes determining a tare weight of a crucible by heatingthe crucible in a muffle furnace for 30 minutes at about 980° C.,cooling the crucible to room temperature in the desiccator, andrecording the resulting weight of the crucible as W1. The ash test thenincludes taking a known weight of pattern material (W2), placing it inthe crucible, heating the crucible with a Meeker burner until all thevolatile material has burned off, transferring the crucible to a mufflefurnace (which may be as hot as 100° C.), heating the muffle furnace toabout 980° C. and holding it there for about 30 minutes, allowing thecrucible to cool to about 200° C., transferring the crucible to thedesiccator, and recording the resulting weight of the crucible as W3.The percent ash is equal to (W3−W1)/(W2)×100. The test should be run ontwo samples of the pattern material and only accepted if the two samplesare within a sufficient range of precision (e.g. 0.002% or 0.0005%).

According to some embodiments, the pattern material may be selected tobe a solid at room temperature. According to some embodiments, thepattern material may be selected to have a melting point of at leastabout 140° F. According to some embodiments, the pattern material isselected to have a melting point of at least about 150° F. or at leastabout 160° F. According to some embodiments, the pattern material isselected to have a melting point of up to about 200° F. According toother embodiments, the pattern material is selected to have a meltingpoint of up to about 190° F. or up to about 180° F. In one embodiment,the pattern material has a melting point of about 166° F. to about 176°F.

According to some embodiments, the pattern material may be selected tohave a congeal point of at least about 110° F. According to someembodiments, the pattern material is selected to have a congeal point ofat least about 120° F. or 130° F. According to some embodiments, thepattern material is selected to have a congeal point of up to about 170°F. According to other embodiments, the pattern material is selected tohave a congeal point of up to about 160° F. or up to about 150° F. Inone embodiment, the pattern material has a congeal point of about 138°F. to about 146° F.

According to some embodiments, the pattern material may be selected tohave a ring and ball softening point of at least about 110° F. Accordingto some embodiments, the pattern material is selected to have a ring andball softening point of at least about 120° F. or 130° F. According tosome embodiments, the pattern material is selected to have a ring andball softening point of up to about 170° F. According to otherembodiments, the pattern material is selected to have a ring and ballsoftening point of up to about 160° F. or up to about 150° F. In oneembodiment, the pattern material has a ring and ball softening point ofabout 138° F. to about 146° F.

In some embodiments, the pattern material has a hardness such that ithas a penetration (with a 450 gram load and ASTM D5 needle), of at leastabout 10 DMM (tenths of a millimeter). In some embodiments, the patternmaterial has a hardness such that it has a penetration (with a 450 gramload), of up to about 20 DMM. In some embodiments, the pattern materialcomprises a penetration of 11 DMM to 19 DMM.

In some embodiments, the pattern material has a deflection of no morethan about 0.5 inches. In other embodiments, the pattern material has adeflection of up to about 0.1 inches or up to about 0.08 inches. In someembodiments, the pattern material has a deflection of at least about0.01 inches. According to other embodiments, the pattern material has adeflection of at least about 0.05 inches. Deflection can be measured bysuspending a wax bar that is 0.25 inch thick by 1.5 inches wide 5.75long and suspended 5 inches. The wax bar is weighted on the end with a40 gram weight. The deflection is the amount bar has moved in a setamount of time say 4 hours.

According to some embodiments, the pattern material has a modulus ofrupture of at least about 5 pounds. According to some embodiments, thepattern material has a modulus of rupture of at least about 10 pounds orat least about 14 pounds. According to some embodiments, the patternmaterial has a modulus of rupture of up to about 25 pounds. According tosome embodiments, the pattern material has a modulus of rupture of up toabout 20 pounds or up to about 16 pounds.

According to some embodiments, the pattern material has a brittleness ofabout 5 to 20 inches. According to some embodiments, the patternmaterial has a brittleness of no less than about 10 inches. According tosome embodiments, the pattern material has a brittleness of no more thanabout 15 inches.

In common embodiments, the pattern material is a wax-based material. Thewax-based material may comprise one or more mineral waxes, naturalwaxes, and/or other waxes. The pattern material according to theseembodiments may comprise about 1 wt. % to about 99 wt. % wax. In someembodiments, the pattern material comprises at least about 15 wt. % waxor at least about 30 wt. % wax. In some embodiments, the patternmaterial comprises no more than about 50 wt. % or no more than about 40wt. % wax. In one embodiment, the pattern material comprises about 25wt. % wax.

Some examples of mineral waxes include mineral waxes such as montan wax,peat wax, and petroleum waxes (petrolatum, paraffin wax, ozokerite, andceresin waxes). Petroleum wax is a commonly used mineral wax. Petroleumwax can be a by-product of the petroleum refining process. The qualityand quantity of the wax obtained from the refining process is dependentupon the source of the crude oil and the extent of the refining. Thepetroleum wax component of the wax composition may include, for example,a paraffin wax, including medium paraffin wax, microcrystalline paraffinwax or a combination thereof. However, petroleum wax obtained from crudeoil refined to other degrees may also be used.

Although the exact chemical compositions of these waxes are not known asthe nature of these by-products vary from one distillation process tothe next, these waxes tend to be composed of various types ofhydrocarbons. For example, medium paraffin wax is generally composedprimarily of straight chain hydrocarbons having carbon chain lengthsranging from about 20 to about 40, with the remainder typicallycomprising isoalkanes and cycloalkanes. The melting point of mediumparaffin wax is typically about 50° C. to about 65° C. Microcrystallineparaffin wax is generally composed of branched and cyclic hydrocarbonshaving carbon chain lengths of about 30 to about 100 and the meltingpoint of the wax is typically about 75° C. to about 85° C. Furtherdescriptions of the petroleum wax that may be used may be found inKirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Volume24, pages 473-76, which is hereby incorporated by reference.

Natural waxes and synthetic waxes may also be used to form the wax-basedpattern material. For instance, many creatures (such as insects andanimals) and plants form waxy substances that are generally solid atroom temperature. Some example of the various types creature waxes arebeeswax, lanolin, shellac wax, chinese insect wax, and spermaceti. Someof the examples of the various types of plant waxes are camauba,candelila, japan wax, ouricury wax, rice-bran wax, jojoba wax, castorwax, bayberry wax, sugar cane wax, and maize wax. Additionally,synthetic waxes may be used. For instance, waxes such as polyethylenewax, Fischer-Tropsch wax, chlorinated naphthalene wax, chemicallymodified wax, substituted amide wax, alpha olefins and polymerized alphaolefin wax may be used. Waxes may also include waxes formed fromchemically modified fatty acid esters, such as dehydrogenated palm oiland/or soybean oil. The wax may also comprise free fatty acids.

In some exemplary pattern materials, particular wax-based patternmaterials, the pattern material comprise fillers. Fillers may beparticles and may be used to control an amount of shrinkage of thepattern material. Exemplary fillers that may be used include acidicfillers (e.g. Terephthalic acid), acrylic fillers, polystyrene (e.g.cross-linked polystyrene), water, and bisphenol-A. In some embodiments,the pattern material may comprise at least about 10 wt. % filler. Inother embodiments, the pattern material may comprise at least about 15wt. % or at least about 20 wt. % filler. In some embodiments, thepattern material may comprise no more than about 50 wt. % filler. Inother embodiments, the pattern material may comprise no more than about40 wt. % or about 30 wt. % filler. In some embodiments, fillers may beused to reduce linear or volumetric contraction, increase viscosity,and/or control dimensions.

In some exemplary pattern materials, particularly wax-based patternmaterials, the pattern material may comprise resin. Exemplary resinsthat may be used include ethylene vinyl acetate, hydrocarbon resins(e.g. C5 or C9 hydrocarbon resins), terpene resins, coal tar derivedresins, and rosins. In some embodiments, the pattern material maycomprise at least about 10 wt. % resins. In other embodiments, thepattern material may comprise at least about 20 wt. % or at least about30 wt. % resins. In some embodiments, the pattern material may compriseno more than about 60 wt. % resins. In other embodiments, the patternmaterial may comprise no more than about 50 wt. % or up to about 40 wt.% resins. In some embodiments, resins may be used to reduce shrinkageand/or impart strength, rigidity, and/or hardness to a pattern formed bythe pattern material.

In some exemplary patterns materials, the pattern material may include adye or a pigment, which may be used to help identify one formulation ofwax from a different formulation of wax.

A suitable wax-based material for use in investment casting may bepurchased from Argueso under the trade name Cerita Pattern Waxes. Othersuitable waxes may be obtained from Westech Products, J. F. McCaughlin,Blayson Olefines, and Blended Waxes, Inc.

Referring to FIG. 1, a method for performing investment casting includesforming the pattern material at block 10. The pattern material may beconfigured as described above. In some embodiments, the pattern materialis wax-based. As discussed above, the wax-based pattern material mayinclude an additive, such as a fluorochemical, to give the patternmaterial better internal mold release. In the case of a wax-basedpattern material comprising a fluorochemical additive, the additive canbe added directly to the wax at time of blending the melt or high shearmixed into the final melted pattern wax with aid of a high shear mixer.This can produce a pattern wax with very fine droplets of thefluorochemical dispersed in a pattern wax.

Once the pattern material is formed, the pattern itself may be formed atblock 20. This may comprise injecting pattern material in a fluid state(e.g. liquid or paste) into a die (e.g. using an injection press),allowing the pattern material to enter a solid state, ejecting the solidpattern from the die, and/or further cooling the pattern (e.g. using awater bath). U.S. Pat. No. 4,971,547 describes one exemplary method andsystem for forming a pattern from a pattern material, the disclosure ofwhich is hereby incorporated by reference.

In some embodiments, the pattern material injection pressure may beabout 240 to about 590 psi. In some embodiments, the pattern materialinjection pressure may be less than about 510 psi. In other embodiments,the pattern material injection pressure may be less than 300 psi.

In embodiments where an additive is used to increase the internal moldreleasability of the pattern material, the pattern material with theadditive may require less injection pressure than the same compositionexcluding the additive. In some embodiments, the pattern material withthe additive requires a pattern material injection pressure that is lessthan 90% of the pattern material injection pressure required for thesame pattern material composition without the additive. In someembodiments, the pattern material with the additive requires less thanabout 85%, or less than about 80% of a pattern material injectionpressure than without the additive.

In embodiments where an additive is used to increase the internal moldreleasability of the pattern material, an additive may be selected whichtends to migrate to the surface of the pattern. In other words, theadditive would tend to have a higher concentration on the surfaces ofthe pattern than in the center of the pattern.

Each pattern may include one or more gates, potentially located at theheaviest (thickest) portion of the pattern. Gates may be wax projectionswhich may be used to attach the pattern to a sprue. A sprue is aconnector (generally comprising a non-filled pattern material) used tofasten patterns together to form a mold. Sprues may vary in size andshape and may accommodate as few as one pattern. In some embodiments, asprue is connected to at least about 30 patterns or at least about 100patterns (and potentially several hundred). A pouring cup may be securedto the central sprue of the mold.

According to some embodiments, a pattern has a weight of about 3 toabout 15 grams. According to some embodiments, the pattern has a weightof about 10 to about 40 grams. According to some embodiments, thepattern has a weight of about 35 to about 100 grams. According to someembodiments, the pattern has a weight of about 100 grams to 1000 grams.According to some embodiments, the pattern has a weight of more than1000 grams. Some patterns may even weigh over 30,000 grams.

Once the pattern is formed, a shell is formed at block 30. The patternmay be dipped in or otherwise coated with one or more ceramic slurries.While it is advantageous to pick a pattern material with good moldreleasability, it is also important to pick a pattern material which hassufficient adhesion with the shell forming material so that the shape ofthe pattern will be accurately reproduced. Excess slurry may be drainedoff and the cluster may be coated with a fine ceramic sand and dried.The coating process may be repeated, and may use progressively coarsergrades of ceramic material. The shell may have a thickness of at leastabout 0.25 inches. In some embodiments, the shell has a thickness ofabout 0.2 inches to about 0.5 inches.

An exemplary process for forming a shell may include dipping a mold in aslurry consisting of either zircon or silica powder with colloidalsilica as binder, styrene butadiene polymer, wetting aids, and biocide,followed by a sand such as zircon or fused silica. The shell is dried.This may be followed by a slurry consisting of fused silica, colloidalsilica, polymer wetting aids, and biocide, followed by a sand such asfused silica. The shell is then dried and the process may be repeateduntil a desired shell thickness is achieved. This process allows forgood adhesion of the prime layers to the exemplary patterns disclosedbelow. According to some exemplary embodiments, adhesion of the primelayer to the pattern material with the internal mold release additive isequal to or greater than the same pattern materials without an internalmold release additive which have been made using a silicon sprayexternal mold release agent.

Once the shell is formed, the pattern material may be removed at block40. The coated pattern may be placed in a furnace, steam autoclave, orother system where the pattern material, including any additives, meltsand flows out of the mold through the pouring cup. The result should bea shell corresponding to the shape of the pattern. The shell may then befired to burn out the last traces of pattern material and to preheat themold in preparation for casting. The pattern material is generallyconfigured to have little expansion when it is melted. This is generallydone so that melting of the pattern does not cause cracking or otherdefects in the shell formed around the pattern. The pattern material isalso generally configured to have a low viscosity at the conditions(temperature, etc.) at which the pattern material is removed from theshell.

Once the pattern material is removed from the shell, the shell isheated, and the finished item is cast at block 50. Molten metal ispoured into the shell. When the metal is cooled, the shell may beremoved (e.g. mechanically or by high pressure water jets).

The formed product may then be finished at block 60. Finishing mayinclude treating the metal to impart desired properties, machining theproduct, painting the product, plating the product, and/or performingsome other steps to finalize the product.

When the pattern material is removed at block 40, it may be recovered atblock 70 for reuse in the investment casting process. Recovering mayinclude removing (e.g. boiling off) any water that may be included inthe pattern material. If water is removed and an additive is used toimpart the internal mold releasability, the additive may be selected tohave a higher boiling point than water and/or is otherwise selected tonot be lost in significant amounts during the water removal process.Recovering may also include filtering, decanting, and/or performing someother process on the pattern material to remove particulate matter fromthe recovered pattern material.

The recovered pattern material may have components refreshed at block80. This may be needed, for instance, if the filtering process wouldremove a filler or resin from the pattern material, and/or ifsignificant amounts of a mold release additive is lost during therecovery process (such as during water removal).

Referring to FIG. 2, a ring-shaped pattern may be formed from patternmaterial by an exemplary molding system 100. Pattern material flows froma source 102, through an injection runner 104 into a die cavity 120.Pattern material enters cavity 120 by way of casting gate 112. Thepattern material is then split around pin 110 and flows left 106 andright 108 through cavity 120. In this embodiment, left 106 and right 108flows reunite at junction 113 on the other side of pin 110 from gate112. If something prevents left 106 and right 108 flows from joiningproperly, a knit line may be created in the pattern formed from themold. If the knit line is capable of being reproduced in latter steps ofthe investment casting process, the knit line may be referred to as anopen knit line. Such open knit lines create visual defects and may be asource for structural weakness as well.

According to many exemplary pattern materials described herein, thepattern material may be configured to avoid the formation of open knitlines. According to some embodiments, the pattern material may be usedto form at least about 100 patterns without open knit lines. Accordingto some embodiments, the pattern material may be used to form at leastabout 1000 patterns without open knit lines.

According to many embodiments, the pattern material may be configuredsuch that it is capable of avoiding lines as discussed in the previousparagraph in a die for a typical part used for investment casting.According to some embodiments, the pattern material may be configuredsuch that it is capable of avoiding lines as discussed in the previousparagraph in a die for a complicated part (e.g. a part having at leastthree pins around which the pattern material must flow). According tosome embodiments, the pattern material may be configured such that it iscapable of avoiding lines as discussed in the previous paragraph in adie for a part having a deep draw (e.g. a wall ¼ inch across, 1.5 inchesdeep, and about 90 degrees to the parting line). According to someembodiments, the pattern material may be configured such that it iscapable of avoiding lines as discussed in the previous paragraph in adie for a part meeting a combination of two or more of these parameters.It should be noted that a pattern material may be used in a die meetingsome or none of the above-mentioned parameters, but still be configuredsuch that it is capable of demonstrating one or more of these propertiesin a die according to one or more of the above mentioned parameters.

Patterns may also be subject to flow lines, which are similar to knitlines except they result from the flow characteristics of the patternmaterial. According to some embodiments, the pattern material may beused to form at least about 100 patterns without flow lines. Accordingto some embodiments, the pattern material may be used to form at leastabout 1000 patterns without flow lines.

According to many embodiments, the pattern material may be configuredsuch that it is capable of avoiding lines as discussed in the previousparagraph in a die for a typical part used for investment casting.According to some embodiments, the pattern material may be configuredsuch that it is capable of avoiding lines as discussed in the previousparagraph in a die for a complicated part (e.g. a part having at leastthree pins around which the pattern material must flow). According tosome embodiments, the pattern material may be configured such that it iscapable of avoiding lines as discussed in the previous paragraph in adie for a part having a deep draw (e.g. a wall ¼ inch across, 1.5 inchesdeep, and about 90 degrees to the parting line). According to someembodiments, the pattern material may be configured such that it iscapable of avoiding lines as discussed in the previous paragraph in adie for a part meeting a combination of two or more of these parameters.It should be noted that a pattern material may be used in a die meetingsome or none of the above-mentioned parameters, but still be configuredsuch that it is capable of demonstrating one or more of these propertiesin a die according to one or more of the above mentioned parameters.

In some embodiments, the pattern material may be used such thatsubstantially no flow or knit lines are present in the resulting seriesof patterns. Substantially no flow lines or knit lines can be determinedby comparison to a pattern wax configured as follows: Component PercentComposition Bis-phenol A 10-20 Terephthalic acid 3-7 Cross-linkedpolystyrene 10-30 Paraffin wax 15-25 Microcrystalline Wax  5-10 NaturalWax(Candelilla) 1-5 Polymer(polyethylene) 0.5-1.5 Carboxylicacid(Stearic Acid) 1-5 Modified oxidized hydrocarbon 637891-75-2 1-5Hydrocarbon Resin 69430-35-9 10-20 Hydrocarbon Resin 62258-49-5 15-30Hydrocarbon Resin 69430-35-9  5-10 Resin Ethylene Vinyl Acetate <0.5

Substantially no flow lines or knit lines exist when the total number offlow lines or knit lines is less than or equal to half the number offlow lines formed by a same pattern using the above-listed pattern wax.

Determining whether flow lines or knit exist is limited to dies whichare susceptible to flow lines and knit lines. In many exemplaryembodiments, the die used to form the pattern comprises at least one pinaround which the pattern material must flow. In some exemplaryembodiments, the die used to form the pattern is used to form acomplicated part (e.g. a part having three pins around which the patternmaterial must flow).

The following examples are presented to illustrate some embodiments andto assist one of ordinary skill in making and using the same. Theexamples are not intended in any way to otherwise limit the scope of theinvention claimed in the claims.

EXAMPLE 1

12.4 gram (0.35%) of Fluoroguard™ PCA (DuPont) was added to 3555 gramsof molten pattern wax (Cerita™ F2010 from Argueso) at 185 deg F. Thiswas mixed well for 10 minutes with a high speed mixer. It was cooled to165 deg F., poured into a water jacketed shot chamber and conditioned 16hours at 118 Deg F.

This composition was placed into an injection press and injected into analuminum die to make solid and hollow cylinders. Over thirty-sixconsecutive injections were conducted with no external mold releasebeing added (e.g. sprayed). The 4-inch sliding core operated well withno sticking and no deformation of the part. An excellent patternresulted with no open knit or flow lines.

EXAMPLE 2

A control wax as described above in Example 1 with no Fluoroguardadditive was handled as discussed above in example 1. The control waxstuck in the die by fourth injection. The sliding core could not beretracted without deformation of part.

EXAMPLE 3

The same as example 2, except that silicone was sprayed on the aluminumdie prior to injection every other pattern. Open knit lines resulted inpatterns after spraying the silicone.

EXAMPLE 4

Handled in the same manner as Example 1 except added 17.5 grams (0.5%)of Fluoroguard™ PRO (DuPont) to 3500 grams of molten pattern wax(Cerita™ F2010 from Argueso). An excellent pattern resulted with overeighteen consecutive patterns produced with no sticking.

EXAMPLE 5

Same as Example 1 except added 16.7 grams (0.5%) of Fluoroguard™ FSM(Dupont) to 3340 grams of molten pattern wax (Cerita™ F2010 fromArgueso). An excellent pattern resulted with over twenty-four patternswith no core sticking and absence of open knit lines.

EXAMPLE 6

An exemplary wax-based pattern material may be formed by high shearmixing 0.1 to 1 wt. % Fluoroguard™ PCA with 99.0 to 99.9 wt. % wax-basepattern wax having the following composition: Component PercentComposition Bis-phenol A 10-20 Terephthalic acid 3-7 Cross-linkedpolystyrene 10-30 Paraffin wax 15-25 Microcrystalline Wax  5-10 NaturalWax(Candelilla) 1-5 Polymer(polyethylene) 0.5-1.5 Carboxylicacid(Stearic Acid) 1-5 Modified oxidized hydrocarbon 637891-75-2 1-5Hydrocarbon Resin 69430-35-9 10-20 Hydrocarbon Resin 62258-49-5 15-30Hydrocarbon Resin 69430-35-9  5-10 Resin Ethylene Vinyl Acetate <0.5

EXAMPLE 7

Similar to Example 1, except 0.3 wt. % Fluorad™ FC4430 (3M) (now Novec™FC-4430) was added instead of Fluoroguard™ PCA. The solid and hollowcylinders could be injected 10 times before core sticking began tooccur, the 10 times delivering excellent pattern quality.

EXAMPLE 8

Similar to Example 6, except 0.5 wt. % of Zonyl® PFSO100 (DuPont) wasadded instead of Fluoroguard™ PCA. The solid and hollow cylinders couldbe injected 5 times before core sticking and pattern distortion began tooccur.

EXAMPLE 9

Similar to Example 6, except that 0.4 wt. % Fluorad™ FC4432 (3M) (nowNovec™ FC-4432) was added instead of Fluoroguard™ PCA. The solid andhollow cylinders could be injected up to 8 times before core stickingand pattern distortion began to occur.

EXAMPLE 10

Similar to Example 1, except that 0.6 wt. % Fluorogurd™ PRO (DuPont) wasadded instead of Fluoroguard™ PCA. The wax was melted and conditionedwith a heat exchanger, similar to that described in U.S. Pat. No.4,971,547, prior to being injected into dies by an automatic press. Highquality patterns resulted showing no open knit lines nor open flowlines. Forty-six different dies were tested using this pattern material.Of these, six dies continued to require spraying of a silicone moldrelease agent, but were able to form 3 to 5 times as many patternsbetween spraying. Many of the tested dies were used to form multiplehundreds of consecutive quality parts without the need for an externalmold release agent.

1. A wax-based pattern material for use in investment casting,comprising: a wax; and a fluorochemical; wherein the pattern material issuitable for use in investment casting.
 2. The pattern material of claim1, further comprising a filler.
 3. The pattern material of claim 2,wherein the filler comprises at least two different types of filler. 4.The pattern material of claim 1, further comprising a resin.
 5. Thepattern material of claim 4, further comprising a filler.
 6. The patternmaterial of claim 1, further comprising an ash content of less thanabout 0.02%.
 7. The pattern material of claim 1, further comprising ashrinkage of no more than about 0.01 inch per inch.
 8. A wax-basedpattern material for use in investment casting, comprising: about 15 wt.% to about 50 wt. % wax; about 10 wt. % to about 60 wt. % resins; and afluorochemical, fluorochemicals comprising less than about 5 wt. %. 9.The pattern material of claim 8, further comprising an ash content ofless than about 0.02%.
 10. The pattern material of claim 8, furthercomprising about 10 wt. % to about 50 wt. % filler.
 11. The patternmaterial of claim 8, comprising about 20 wt. % to about 50 wt. % resins.12. The pattern material of claim 8, comprising less than about 1 wt. %fluorochemicals.
 13. A composition for use in investment casting,comprising: a pattern material, the pattern material comprising internalmold releasability; and wherein the composition is suitable for use ininvestment casting.
 14. The composition of claim 13, wherein the patternmaterial comprises a wax, an additive that contributes to the internalmold releasability, and a resin.
 15. The composition of claim 13,wherein the pattern material is configured to have sufficient internalmold releasability such that a die can use the pattern material at leastabout 20 times without requiring application of an external mold releaseagent.
 16. The composition of claim 15, wherein the pattern material isconfigured to have sufficient internal mold releasability such that adie comprising a deep draw can use the pattern material at least about20 times without requiring application of an external mold releaseagent.
 17. The composition of claim 15, wherein the pattern materialcomprises sufficient adhesion to a ceramic slurry to form a shell. 18.The composition of claim 13, wherein the pattern material comprises anadditive that contributes to the internal mold releasability, theadditive selected such that the additive has a higher concentration onsurfaces of a pattern molded using the composition than in an interiorof the pattern.
 19. The composition of claim 13, further comprising afluorochemical which contributes to the internal mold releasability ofthe pattern material.
 20. The composition of claim 13, wherein thepattern material comprises a shrinkage of no more than about 0.01 inchper inch.
 21. The composition of claim 13, further comprising an ashcontent of less than about 0.02%.
 22. The composition of claim 13,wherein the composition is solid at room temperature.
 23. Thecomposition of claim 13, wherein the composition comprises an additivethat contributes to the internal mold releasability of the patternmaterial, wherein the additive contributes to the internal moldreleasability of the pattern material such that the pattern materialwith the additive may be used to make at least about three times as manyconsecutive quality parts as the same pattern material without theadditive.
 24. A method of investment casting, comprising: forming apattern using a pattern material, the pattern material comprisinginternal mold releasability; forming a shell using the pattern; removingthe pattern material from the shell; and casting a product using theshell.
 25. The method of claim 24, wherein the pattern materialcomprises a wax and a resin.
 26. The method of claim 24, wherein thepattern material comprises a fluorochemical.
 27. The method of claim 24,further comprising recovering the pattern material removed from theshell.
 28. The method of claim 24, wherein the pattern material is solidat room temperature.
 29. The method of claim 24, wherein forming apattern using a pattern material does not comprise applying an externalmold release agent to a die used to form the pattern.
 30. The method ofclaim 24, wherein the pattern material is configured to have sufficientinternal mold releasability such that a die can use the pattern materialat least about 40 times without requiring application of an externalmold release agent.
 31. A method of investment casting, comprising:forming a pattern using a pattern material, forming a pattern using apattern material not comprising applying an external mold release agentto a die used to form the pattern more than once every 100 shots;forming a shell using the pattern; removing the pattern material fromthe shell; and casting a product using the shell.
 32. The method ofclaim 31, wherein the pattern material comprises a wax and a resin. 33.The method of claim 32, wherein the pattern material further comprises afiller.
 34. The method of claim 32, wherein the pattern materialcomprises a fluorochemical.
 35. The method of claim 31, furthercomprising recovering the pattern material removed from the shell. 36.The method of claim 31, wherein the pattern material is solid at roomtemperature.
 37. The method of claim 31, wherein forming a pattern usinga pattern material does not comprise applying an external mold releaseagent to a die used to form the pattern.
 38. A method of investmentcasting, comprising: forming a pattern using a pattern material, forminga shell using the pattern; removing the pattern material from the shell;and casting a product using the shell; wherein substantially no flow oropen knit lines are formed in the pattern.
 39. The method of claim 38,wherein a die is used to form the pattern and the die comprises at leastone pin around which the pattern material must flow.
 40. The method ofclaim 38, wherein the product cast using the shell comprises acomplicated part.
 41. The method of claim 38, wherein forming a patternusing a pattern material not comprising applying an external moldrelease agent to a die used to form the pattern more than once every 100shots.
 42. The method of claim 38, wherein the pattern materialcomprises internal mold releasability.
 43. The method of claim 38,wherein the pattern material comprises a wax and a resin.
 44. The methodof claim 38, wherein the pattern material comprises a fluorochemical.45. The method of claim 38, wherein the pattern material comprises anadditive that contributes to internal mold releasability of the patternmaterial, the additive selected such that the additive has a higherconcentration on surfaces of a pattern molded using the composition thanin an interior of the pattern